1. Field of the Invention
The present invention relates to a display device including a plurality of pixels and a plurality of memory cells. The present invention also relates to an electronic appliance using the display device having a plurality of pixels and a plurality of memory cells.
2. Description of the Related Art
In recent years, development of a display device including various kinds of circuits provided over a substrate has been carried out. For example, there is a monolithic display device in which an active matrix circuit for displaying images and a driving circuit for controlling the operation of the active matrix circuit are provided over a same substrate (e.g., see the patent document 1).    [Patent Document 1]: Japanese Patent Application Laid-Open No. Hei 10-228248
When a memory circuit for storing data is provided together with a pixel portion for displaying images and a driving circuit for controlling the operation of the pixel portion over a substrate, a high performance, multifunction and high-value-added display device can be provided. As the memory circuit, a DRAM (dynamic random access memory), an SRAM (static random access memory), an FeRAM (ferroelectric random access memory), a mask ROM (read only memory), an EPROM (electrically programmable read only memory), an EEPROM (electrically erasable read only memory), a flash memory and the like can be given. The DRAM and the SRAM are volatile memories and have a drawback in that when turning the power off, data must be rewritten in the memories. The FeRAM is a nonvolatile memory and has a drawback of increasing the number of manufacturing steps since a capacitor element including a ferroelectric layer is used. The mask ROM includes a simple structure; however, it has a defect in that data must be written during the manufacturing process and new data cannot be written in the mask ROM additionally. The EPROM, the EEPROM and the flash memory are nonvolatile memories; however, since they use elements each including two gate electrodes, they has a drawback of increasing the number of manufacturing steps.